1. Technical Field
The invention relates to the enhancement of text in a computer environment. More particularly, the invention relates to the enhancement of the text of a digitally scanned document in a computer environment.
2. Description of the Prior Art
Text or pictorial images are often replicated or transmitted by a variety of techniques, such as photocopying, facsimile transmission, and scanning images into a memory device. The process of replication or transmission often tends to degrade the resulting image due to a variety of factors. Degraded images are characterized by indistinct or shifted edges, blended or otherwise connected characters and distorted shapes.
A reproduced or transmitted image that is degraded in quality may be unusable in certain applications. For example, if the reproduced or transmitted image is to be used in conjunction with a character recognition apparatus, the indistinct edges, connected characters, etc. may preclude accurate or successful recognition of characters in the image. Also, if the degraded image is printed or otherwise rendered visible, the image may be more difficult to read and less visually distinct.
There are several approaches to improve image quality. A classical resolution enhancement algorithm is template matching. Template matching attempts to match a line, curve pattern, or linear pattern and then tries to find the best way to reconstruct it with the printing resolution.
Other methods for text enhancement come from the area of Optical Character Recognition (OCR). The main purpose is to isolate the characters from one another. The concern is not for enhancement. The methods apply more to morphological filters which repetitively perform thickening and thinning and opening and closing to get the desired character shape.
U.S. Pat. No. 5,351,314 issued to Vaezi on Sep. 27, 1994, is a method for image enhancement involving the smoothing and thinning of input image data by applying a filter to each pixel of input image data. Characters are segmented and identified based on a comparison of the segmented character to a dictionary of characters.
U.S. Pat. No. 5,542,006 issued to Shustorovich et al. on Jul. 30, 1996, is a method for use in an OCR system for locating center positions of all desired characters within a field of characters such that the desired characters can be subsequently recognized using an appropriate classification process. This method is used for character recognition and not for text enhancement.
There are also standard sharpening filters that convolve the image with a mask and a low-pass filtering kernel and then perform unsharp masking by a linear combination of the original and the blurred image. Another is just to convolve the image with a sharpening kernel. More sophisticated algorithms apply adaptive methods.
U.S. Pat. No. 5,644,648 issued to Bose et al. on Jul. 1, 1997, is a method for recognizing connected and degraded text that filters a scanned image to determine whether a binary image of an image pixel should be complemented. The pixel is complemented only if doing so does not reduce the sharpness of the wedge-like figures in the image.
Other simplistic approaches would be to threshold the text. A grayscale or color scanning of the text is performed. Some portion of the page is identified that is text and it is then thresholded and white placed where it is light and black where it is gray. This however, does not work.
It would be advantageous to provide a text enhancement system that improves the sharpness of the text of a scanned document by increasing the high contrast boundaries which are perceived as sharpness. It would further be advantageous to provide a text enhancement system that takes advantage of the ink centralization property of text and is independent of the type of scanner used.